The Research Of Key Section Stability Control Of Asynchronous Interconnected Power Grid

With the development of VSC-HVDC(Voltage Source Converter based High Voltage Direct Current),more and more AC transmission systems have been transformed into flexible DC back-to-back transmission systems.After transformation,the sending-end power grid and the receiver-end power grid will be transformed from AC-DC synchronous hybrid mode to DC asynchronous interconnection mode.Then,on the one hand,profound changes have take place in the structure and operating characteristics of the power grids.The original security and stability control measures need to be re-studied for the adaptability of the power grid;on the other hand,although the application of VSC-HVDC can greatly reduce the interaction between the AC power grids on both sides,it restricts the mutual support capabilities of the regional grids in the event of major failures or large disturbances.In view of the problems above,the stability and control of the key section in the asynchronous interconnected power grid is studied in this paper.The main content is as follows:Firstly,the asynchronous interconnected power system with multiple VSC-HVDC lines is built,and the detailed VSC models and load models are established.The transient stability mechanism of the single machine infinite bus system,the equivalent two machine system and the multi machine system is analyzed from the perspective of the inertial time constant of the system.The N-1 fault analysis and N-2 fault analysis are performed offline for the actual power grid to grasp the characteristics of transient stability changes of the regional power grid after asynchronous networking.Secondly,the control strategy for ACE of the automatic generation control system is studied.The dynamic ACE start-up and action logic which takes the power mutation and the power balance as the core is designed.A flexible and diverse dynamic ACE allocation optimization strategy is formulated;The influence of the K-factor on the stability and control of the key section is analyzed and the optimization control method of time-phased K-factor is put forward.Through the simulation conparison of the actual power grids data,the promotion effect of the time-phased K-factor method on the stability of key sections is verified.Finally,a coordinated control strategy of regional dynamic ACE and VSC-HVDC emergency power support is proposed.By analyzing the decoupled control method of the active and reactive power of the VSC-HVDC,the advantage of independent control of active and reactive power is explained.Taking advantage of VSC-HVDC emergency power control,a coordinated control strategy of regional dynamic ACE znd VSC－HVDC emergency power support is formulated.Besides,the simulations are carried out through actual power grids data,which proves that the proposed control strategy can effectively improve the ability to restore stability of the VSC-HVDC asynchronous interconnected system after serious faults.In this paper,the mechanism analysis of transient stability characteristics of regional power grid in asynchronous interconnected system is carried out,the dynamic ACE control strategy of regional power grids is designed,a key section stability control method with time-phased K-factor is put forward,and the coordinated control strategy of regional dynamic ACE and VSC-HVDC emergency power support is formulated.The simulation results show that the stability of asynchronous interconnected grids has been improved.